This invention relates to a tilting mechanism for a marine propulsion device and more particularly to an improved tilt and trim arrangement for an outboard drive.
It has been known to provide various arrangements for adjusting the trim angle of an outboard drive for a marine propulsion unit. The term "outboard drive" as used in the specification and claims hereof, is intended to refer to either the outboard drive portion of an inboard-outboard drive assembly or to an outboard motor per se. Adjustment of the trim angle of the outboard drive is desirable for a number of reasons. For example, when operating in shallow water, it is desired to provide a trim up condition for the outboard drive so as to minimize the likelihood of striking submerged obstacles. It has also been found that it is desirable to adjust the trim angle of the outboard drive in response to the actual speed of travel of the watercraft. The drag resistance of the lower unit is less in a trim down condition than in the trim up condition at certain low speeds. However, as the speed of the watercraft increases, there is a point at which the drag resistance is lowered if the unit is trimmed up.
It is, therefore, a principal object of this invention to provide an improved device for adjusting the trim of an outboard drive.
It is another object of this invention to provide an outboard drive trim adjusting device that is automatic in operation and which provides the minimum flow resistance under all running conditions.
It is another object of this invention to provide a trim adjusting device for a marine propulsion unit that automatically trims the drive up in response to predetermined conditions.
Although it is desirable to provide automatic trim adjustment for the outboard drive, the desirability of providing such automatic trim adjustment varies in response to running conditions. For example, when operating in reverse, it may not be desirable to have the outboard drive trim up automatically. This is true also under some other running conditions.
It is, therefore, a still further object of the invention to provide an automatic trim adjusting device for an outboard drive that is responsive to the specific running conditions.
With many types of outboard drives, it has been proposed to employ a hydraulic piston and cylinder arrangement for controlling both the trim and tilting of the outboard drive. Such arrangements are common with larger horsepower outboard motors and with most inboard-outboard drive arrangements. Normally, a relatively small diameter, fast operating tilt cylinder is employed for tilting the outboard drive from a submerged to a tilted up condition. Larger, slower acting trim cylinders also are employed that act against the outboard drive for adjusting the trim condition. Devices of the type heretofore employed have utilized a single hydraulic control circuit for both the trim and tilt cylinders. This has, therefore, necessitated trimming of the outboard drive through its full range before the motor can be tilted up. Of course, such an arrangement is rather time consuming in achieving the tilting up function.
It is, therefore, a still further object of this invention to provide an improved, simplified and faster acting tilt and trim cylinder arrangement.